1. Field of the Invention
This invention relates to an apparatus for fluid dynamic control and more particularly relates to an apparatus for channeling an exhaust flow.
2. Description of the Related Art
Modern combustion engines meeting rigorous emissions standards often employ various turbocharger schemes to achieve fuel economy, emissions, and power density requirements. A multiple turbocharger system often includes the use of a bypass valve as the first stage turbocharger may be small and not designed for the full air flow of the engine at rated operation. It is often desirable that an engine perform braking functions as well as power functions. In some engines, the engine valve timing is changed such that the engine collects work from the wheels by compressing air within the engine cylinders and venting the still-compressed air. However, engine braking systems are often expensive and in some vehicles the benefits may not support the cost. In some applications, a valve in an exhaust line may perform the functions of the engine braking, which is often called “exhaust braking.” When the valve begins to close, the back pressure begins to increase on the engine, and the pressure losses across the valve consume work and provide a braking function.
The introduction of multiple turbocharger systems complicates the systems of exhaust braking. An exhaust braking valve which is not downstream of the bypass valve is not sufficient to perform the exhaust braking function alone, as the exhaust can flow through a bypass line with relatively low pressure loss. Placing the exhaust brake past all turbochargers will typically allow exhaust braking to perform properly, but this implementation limits the generality of installations, and may require excess wire lengths for exhaust valve actuators and sensors depending upon the availability of a place in the exhaust line that is downstream of the bypass line and turbochargers. Additionally, in some applications it may be useful to block flow through a small turbocharger completely, and this is not available in a bypass system with the exhaust valve completely downstream of the bypass line.
Therefore, current systems require a bypass valve and a separate exhaust braking valve, and further require that the exhaust brake valve be installed in a limited number of positions—specifically downstream of the bypass line.